Nanoscale patterned articles, such as nanoscale gratings and wires, have many important applications in optics, electronics, biotechnology, and micro-fluidics. They can be used to filter and direct light, to facilitate fabrication of nanoscale mechanical and electronic devices, and to analyze biological molecules.
A typical nanoscale patterned article comprises a substrate with a microscopically patterned surface. A nanoscale grating, for example, can comprise a substrate, such as silicon or resist coated silicon, having a surface array of protruding parallel lines separated by intervening recessed lines. The lines can have a minimum dimension of under 100 nanometers and the spacing between successive lines can be on the order of 200 nm or less. Other articles use different surface patterns of comparably small feature size.
The roughness of line edges and sidewalls in such nanoscale surface patterns has an important bearing on device performance. Studies have shown that roughness causes scattering loss in optical devices, impedes electron transport through nano-scale wires and degrades performance in bio-analytic and micro-fluidic systems.
A variety of approaches have been proposed for the fabrication of smooth nanoscale surface patterned devices, but most are unsuitable for large-scale production. Previous fabrication methods include electron-beam lithography and interference lithography. Electron beam lithography, however, is a serial processing technique of inherently low throughput. Interference lithography is affected by random factors such as disturbances and instabilities in the exposure system which contribute to roughness.
Other approaches to reducing roughness include anisotropic wet etching and thermal oxidation of pattern sidewalls with etch-back. Anisotropic wet etching, however, can only be used on a limited class of crystalline materials. And thermal oxidation requires high temperature processing incompatible with many desirable materials.
Nanoimprint lithography (NIL) is a promising approach to patterning smooth nanoscale features. In NIL, a nanofeatured molding surface is typically imprinted into a surface, such as a polymer-coated substrate. The imprinted pattern can then be coated, as with metal, or the imprinted material can be selectively removed to expose the substrate surface for further processing. Further details concerning nanoimprint lithography are set forth in applicant's U.S. Pat. No. 5,772,905 issued Jun. 30, 1998 and entitled “Nanoimprint Lithography” and U.S. Pat. No. 6,482,742 issued Nov. 19, 2002 and entitled “Fluid Pressure Imprint Lithography.” The '905 and '742 patents are incorporated herein by reference.
The present invention provides articles comprising nanoscale patterns with reduced edge and sidewall roughness through adaptations in NIL processing.